Various materials such as concrete materials and the like are used as the floor material of bridges and the like. Steel floor plates are known as one of these materials. Steel floor plates are principally formed by steel plates (i.e., deck plates), however, deck plates themselves can not satisfactorily guarantee the necessary strength. Therefore, normally, steel floor plates are formed as stiffened plates which have stiffener materials (i.e., ribs) provided on their bottom surface.
These stiffener materials may be belt-shaped plate steel, or may be steel materials having a V-shaped or U-shaped cross section which are known as closed cross section ribs or the like. These stiffener materials are joined to the bottom surface of a deck plate in parallel with each other and at fixed intervals so as to form a stiffened plate.
Here, edge portions on both ends of the closed cross section ribs are joined by arc welding to the deck plate so as to form a closed cross-sectional structure with the deck plate.
A variant example of the above described type of stiffened plate is the sandwich panel shown in Non-patent document 1. This sandwich panel is manufactured by arranging a number of U-shaped rib members in parallel with each other on a deck plate so as to form a closed cross-sectional structure, and by then arc welding edge portions of the U-shaped rib members onto the deck plate. In addition, a bottom plate is placed on apex portions of the U-shaped rib members, and the apex portions of the U-shaped rib members and the bottom plate are joined together by laser welding.
Note that Patent document 1 below by the applicants of the present invention provides documentation for prior art relating to welding technologies for stiffened plates.
Non-patent document 1: “Strength Characteristics of Laser Lap Welded Joins in Medium Thickness Plates and Panel Manufacturing”, by Shoichi Kitagawa, Hitachi Zosen Corporation in “Laser Symposium: Applications of Laser Welding to Medium Thickness Plate manufactured Bodies” Corporation: Japan Welding Engineering Society, LMP Committee, convoked Aug. 22 (Th) to 23 (We), 2002
Patent document 1: Japanese Unexamined Patent Application, Publication No. 2006-224137